The present invention relates generally to aerial work platforms and, more particularly, to laterally rotatable work platforms.
Aerial work platforms for the construction industry are typically mounted at the end of a boom that extends outwardly from a wheeled vehicle. The vehicle and the boom are movable to position the work platform at a desired location. The boom can extend and retract to raise and lower the work platform to a desired vertical location. Some work platforms can also be rotated relative to the boom in a lateral plane to point the work platform at a desired angle in the lateral plane relative to the boom. Accordingly, the work platform can be maneuvered to position a user adjacent to an elevated work site.
In one conventional device, the work platform is mounted to the boom of the vehicle with two parallel, pivotable links. The links and the work platform are biased to a horizontal position with a coiled spring. As the load on the work platform is increased, the spring compresses and the parallel links allow the work platform to descend slightly relative to the boom while the work platform remains approximately horizontal. A sensor coupled to the boom can trigger an alarm or a signal when the load on the platform (and therefore the vertical deflection of the platform) exceeds a selected amount. For example, the sensor can include a first switch that triggers an audible alarm when the load on the work platform exceeds a first selected value, and a second switch that shuts down motion of the work platform when the load thereon exceeds a second, greater value. Accordingly, the sensor can warn the user when the load on the work platform approaches a selected capacity and can prevent further movement of the work platform if the selected capacity is exceeded, reducing the likelihood for potential safety hazards associated with using the work platform.
In one aspect of this conventional device, the work platform can be rotated relative to the boom in the lateral plane with a rack and pinion arrangement. For example, a rack can be attached to the work platform and can engage the teeth of a pinion fixedly attached to the boom. As the rack is driven linearly back and forth in the lateral plane relative to the fixed pinion (for example, with a pressurized hydraulic fluid), the rack and the work platform will rotate in the lateral plane about the fixed pinion. Alternatively, the rack and pinion can be replaced with a worm gear drive for rotating the work platform relative to the boom, and/or the two parallel links can be replaced with a single link and a spaced-apart cam and cam follower combination.
One drawback with the foregoing attachment and rotation devices is that they can be heavy. The weight of the devices can reduce the weight that can be allocated to the load on the work platform, in effect reducing the capacity of the work platform. Alternatively, the weight of the devices can limit the lateral distance that the boom can extend relative to the vehicle before the vehicle becomes unstable.
Another drawback is that the foregoing attachment and rotation devices can be bulky, which can make the devices difficult to integrate with the work platform and/or difficult to install and maintain. Furthermore, it can be difficult to shield the bulky conventional devices from inadvertent contact with surrounding structures, making the devices more susceptible to damage during normal use.
The present invention is directed toward fluid-powered, rotatable support platform assembly usable with an assembly support such as a vehicle having an arm for selectively positioning such an assembly. In one embodiment, the assembly can include a load platform having a support surface for supporting a load, a body having a cavity extending along a longitudinal axis of the body, and a shaft rotatably disposed within the body and having a shaft axis generally aligned with the longitudinal axis of the body. One of the body or the shaft is configured to be coupled to the assembly support platform, and the other one of the body and the shaft is configured to provide rotary drive to the load support platform. A linear to-rotary force-transmitting member is positioned within the cavity of the body and is mounted for longitudinal movement within the body generally aligned with the longitudinal axis in response to selective application of pressurized fluid thereto. The force-transmitting member engages the body and the shaft to translate longitudinal motion of the force-transmitting member to rotational movement between the shaft and the body with a rotational force sufficient to selectively rotate the load support platform about the longitudinal axis relative to the assembly support in a rotational plane in clockwise and counterclockwise rotational directions.
A load sensor is positioned to detect a load on the load support platform in a load direction out of alignment with the rotational plane. A platform connector member is coupled between the load support platform and the other one of the body and shaft. The platform connector member is configured to permit movement of the load support platform in the load direction while restricting movement in directions out of alignment with the load direction except rotation of the load support platform in the rotational plane in response to the rotary drive. A load transmission member may be included to transmit the rotary drive to the load support platform.
The assembly can further include a spring positioned between the load support platform and the load transmission member to bias the load support platform in a direction opposite the load direction.